This invention generally relates to navigation or route guidance systems and, more particularly, to a navigation system that provides audible route guidance instructions to a user of the navigation system.
Navigation systems generally provide a recommended route from a starting point to a desired destination. Generally, the starting point and desired destination are selected from a large database of roads stored in a mass media storage, such as a CD ROM, which includes the roads in the area to be travelled by the user. The navigation system can be located in a personal computer or it can be installed in a vehicle. If the navigation system is installed in a vehicle, the starting point is typically the current position of the vehicle, which can be input to the navigation system by an associated position determining system that usually includes a GPS (Global Positioning System) receiver.
The navigation system determines a route from the starting point to the destination utilizing an algorithm well-known to those in the art and currently in use in many navigation systems. Usually there are many potential routes between the selected starting point and the desired destination. Typical navigation systems select a recommended route based upon certain "cost" values associated with each segment of road in the road database. These cost values include the length of the road segment and the estimated time of travel through the road segment. The navigation system selects the potential route with the lowest total cost to be the recommended route. Depending upon the predetermined algorithm of the navigation system, the navigation system will recommend the route with the shortest total length, the lowest total time, or some weighted average of length and time.
The recommended route is then displayed to the user as a map showing the starting point and desired destination and highlighting the recommended route. Preferably, if the navigation system is installed in a vehicle, the navigation system displays the current position of the vehicle and provides visual turn-by-turn instructions to the driver, guiding the driver to the selected destination.
Many navigation systems also provide audible turn-by-turn instructions to the driver. One such system is that disclosed in U.S. Pat. No. 5,406,492 wherein an instruction is perceived by the driver to be emanating from a fixed direction that is determined by the content of the instruction. One disadvantage of such a system is that drivers do not always correctly perceive the direction of the fixed source and thus any benefit derived by associating the source of the instruction with its content is lost.
Thus, it is desirable to provide a system for projecting audible instructions that enhances the ability of a driver to correctly perceive the content of the instruction. It is also desirable to provide a system that is readily adaptable to a typical vehicle audio system.